Conventionally, as a method for packaging food such as processed meat products, seafood paste products, meats, fishes, cheeses, there are generally used a method for filling and packaging the contents into a bag or a pouch bag made of an oriented/shrinkable or a non-oriented/non-shrinkable multilayer film, and a method for filling and packaging the contents into a bag made of a multilayer film just after the bag is formed by a vertical (longitudinal) pillow/transverse (horizontal) pillow type packaging machine. However, in a packaging method using such bags, a method is used in which contents are filled in a bag followed by evacuation at a reduced pressure or vacuum in a vacuum chamber, and thereafter an opening portion is sealed to provide a packaged product, so that, in a series of operations in such bag-type vacuum packaging, increase in a filling rate has limitations. Accordingly, a method that enables an increase in filling rate has been demanded from economical and other point of view.
On the other hand, as a method easily increasing a filling rate compared with the bag-type vacuum packaging method, there is a so-called deep drawing packaging method utilizing vacuum packaging. Generally, non-oriented/non-shrinkable multilayer films are conventionally used for the deep drawing packaging method. Particularly, in the case where irregular shapes of content such as meat, a ham, a roast pork and a bacon are filled and packaged, there are drawbacks that the packaged product is easily wrinkled, and that the films lack in a fitting property for the contents, so that liquid of contents easily stays. Moreover, there is also a drawback that keeping quality of contents becomes poor. In addition, in deep drawing packaging using conventional non-oriented/non-shrinkable multilayer films, a so-called flange portion which is formed by closely attaching a top film with a bottom film not contacting to contents is excessively large, so that there is a problem that it is extremely difficult to obtain a packaging form similar to the bag-type vacuum packaging.
In order to solve these problems, International Application Japanese-Phase Publication No. 2003-535733 (Document 1) discloses a stretch-oriented multilayer film including at least three layers of: a surface layer (a) made of a thermoplastic resin; an intermediate layer (b) made of a polyamide-based resin; and a surface layer (c) made of a sealable resin. The multilayer film exhibits an impact energy of 1.5 Joule or more at a conversion thickness of 50 μm at a temperature of −10° C. In the specification, there is described a deep drawing package using such a stretch-oriented multilayer film.
However, in a deep drawing package, generally, a bottom film having multiple concave portions is formed by deep drawing, and then contents are filled into the concave portions. Then, a non-molded top film is continuously covered onto the concave portions. After the container is evacuated at a reduced pressure or vacuum in a vacuum chamber, deep drawing packaged products are continuously obtained by heat-sealing a peripheral part of an upper face of the bottom film with the top film. Accordingly, even in the deep drawing packaged product described in Document 1 and obtained by using a heat shrinkable film, a seal position of the bottom film and the top film is eccentrically located in the bottom film side. As a result, it is still difficult to obtain a packaging form similar to the bag-type vacuum packaging.